The present invention relates to a method for producing magnetic devices comprising a thin film of magnetic material, such as a magnetic recording thin film medium or other magnetic-related functional devices, having increased orientation ratio without a reduction in surface smoothness.
While magnetic recording media play a core role as an external memory device in computers, the requirements for recording capacity and recording density are increasing year by year.
High coercivity, small Mrt, good coercivity squareness, sufficient thermal stability and high orientation ratio (OR) are normally required for ultra high-density recording media. The orientation ratio is defined for magnetic media as a means to quantify the directional nature of the magnetic properties in the recording medium. The coercivity orientation ratio (ORHC)xe2x80x94ratio of circumferential and radial coercivity on a circumferentially textured diskxe2x80x94is the most often cited. High OR film medium can give sharp transitions, and high signal output as well as low to medium noise. Furthermore, it has recently found that high orientation ratio (OR) can enhance the thermal stability of media.
With the latest developments in thin film media technology, orientation ratio has become an increasingly important factor. Reference is made to an article in J. Apply. Physics, Vol. 87, No. 8 entitled xe2x80x9cEffect of magnetic anisotropy distribution in longitudinal thin film mediaxe2x80x9d.
Another key factor which influences the recording density of a magnetic recording medium is the so-called flying height of the magnetic head. The recording density of a magnetic recording medium is inversely proportional to the flying height of the magnetic head, via which the information is recorded onto and read and/or from the recording medium. The lower the flight height, the higher the writing field that is applied onto the media. Media with high coercivity can be used to get short transition and thus high density. Consequently, in designing computer disks, the flying height of the magnetic head should be reduced as much as possible, in order to increase the recording density. The surface of the disk substrate should be extremely smooth to permit a lower flying height.
However, extreme smoothness can result in a high contact area between the disk and the magnetic head which, in turn, can lead to a high degree of stiction and/or friction during the start up and the stopping of the disk. The high degree of stiction or friction can cause damage to the disk, the recording head and its accompanying assembly, as well as the disk drive motors. These problems counteract against the requirement for increased recording density by increasing the smoothness of the surface of the magnetic recording medium.
Usually, magnetic recording media have a magnetic film as thin as 10-20 nm so that the surface property of the media depends on the surface property of the substrate. To facilitate the retention of lubricant on the magnetic medium surface and thus lower the stiction and/or friction, a controlled surface topology, or the so-called xe2x80x9ctexturexe2x80x9d substrate is often required. The texturing process is primarily a mechanical operation in which uniform, controlled scratches are cut into the polished surface of the substrate such as a nickel-phosphorous alloy coating. It is understood that the texturing of the substrate surface can decrease the true contacting area between the magnetic head and the disk. Furthermore, these scratches result in magnetic orientation along the scratches. Thus, the orientation ratio (OR) is closely associated with the substrate surface roughness induced by the texturing. This kind of circumferential texturing of the substrate can induce orientated magnetic properties in the circumferential direction.
The current texture process is usually accompanied by the formation of weldments and asperities along the texture lines. These weldments and asperities can result in an increase in the required flying height as well as severe wear on the magnetic layer during the operation of the disk. It is normally extremely difficult to obtain a good balance between the incompatible requirements for increased recording density and inducing high orientation ratio (OR) and medium tribology by virtue of the texturing process only.
It is an aim of the present invention to at least partially solve the above-identified problem.
According to a first aspect of the present invention, there is provided a method of producing a thin film magnetic device comprising forming a thin film of magnetic material over a surface of a substrate having a controlled surface topography, wherein the surface of the substrate is first subject to isotropic etching so as to increase the capacity of the substrate surface to induce a high orientation ratio in a thin film of magnetic material formed over the substrate surface without a reduction in the smoothness of the substrate.
According to a second aspect of the present invention, there is provided a method of increasing the capacity of a substrate to induce high orientation ratio (OR) in a thin film of magnetic material formed over a surface of the substrate without reducing the smoothness of the substrate, the method comprising the step of subjecting a surface of a substrate having a controlled surface topography to plasma etching so as to increase the capacity of the substrate surface to induce a high orientation ratio in a thin film of magnetic material formed over the substrate surface without reducing the smoothness of the substrate.
The isotropic etching is preferably such as to also increase the smoothness of the substrate surface and also increase the capacity of the substrate surface to induce coercivity in a thin film of magnetic material formed over the substrate surface.
The term isotropic etching refers to an etching process in which the vertical and horizontal removal of material proceed at substantially the same rate.
The substrate may comprise a substrate base having an upper surface, the upper surface of the substrate base being subjected to the isotropic etching. It may also comprise a substrate base and a seed layer formed on the substrate base, the surface of the seed layer opposite to the substrate base being subjected to the isotropic etching. Alternatively, it may comprise a substrate base, a seed layer formed on the substrate base, and an underlayer formed on a surface of the seed layer opposite the substrate base, the surface of the underlayer opposite the seed layer being subjected to the isotropic etching. According to another embodiment, the substrate comprises a substrate base, a seed layer formed on the substrate base, an underlayer formed on a surface of the seed layer opposite the substrate base, and an intermediate layer formed on a surface of the under layer opposite the seed layer, the surface of the intermediate layer opposite the under layer being subjected to the isotropic etching.
The substrate preferably comprises a coating of a nickel-phosphorous alloy or other suitable alloy on a base material selected from the group consisting of aluminium, an aluminium alloy, glass, ceramics, carbon, glass-ceramic, titanium and silicon, and wherein a surface of the coating opposite the base material is the substrate surface subject to isotropic etching.
According to a third aspect of the present invention, there is provided a method of modifying a thin film magnetic device comprising a thin film of a magnetic material, the method comprising the step of subjecting a surface of the thin film magnetic device having a controlled surface topology to isotropic etching so as to increase the orientation ratio of the thin film magnetic device without reducing the smoothness of the surface of the thin film magnetic device.
According to a fourth aspect of the present invention, there is provided a method of increasing the orientation ratio of a thin film magnetic device comprising a thin film of a magnetic material without reducing the smoothness of the surface of the thin film magnetic device, the method comprising the step of subjecting a surface of the thin film magnetic device having a controlled surface topology to isotropic etching so as to increase the orientation ratio of the thin film magnetic device without reducing the smoothness of the surface of the thin film magnetic device.
In one embodiment, the surface of the thin film of magnetic material is subject to the isotropic etching, whereas in another embodiment, a protective overcoat is formed over the thin film of magnetic material and a surface of the protective overcoat opposite the thin film of magnetic material is subject to the isotropic etching so as to increase the orientation ratio of the thin film of magnetic material without reducing the smoothness of the surface of the protective overcoat.
In each of the above aspects of the present invention, the isotropic etching is preferably carried out by RF sputtering etching, DC or AC plasma etching or reactive ion etching. The isotropic etching may be controlled with respect to an etching parameter selected from base pressure, gas composition, plasma power and etching time.
According to one embodiment, the controlled surface topology is a groove structure.
In a preferred embodiment, one or more of the seed layer, underlayer and intermediate layer, thin magnetic film and protective overcoat are formed by a deposition process, and the deposition process and the isotropic etching are carried out in a single vacuum system.
According to the method of the present invention, weldments and asperities produced in the texturing process are also reduced. The method of the present invention does not damage the original pattern of texture whereby the tribology requirements are fulfilled. Magnetic recording medium prepared using the method of the present invention have been found to have optimized texture morphology. A circumferential coercivity increase of about 1000 Oe, and an OR increase of from 1.2 to 2 have been achieved.
The isotropic etching can be performed in a sputtering apparatus, and it can be readily incorporated into the process of manufacturing magnetic recording media.
In a preferred embodiment of the present invention, a textured nickel-phosphorous (Nixe2x80x94P) alloy layer plated on an Alxe2x80x94Mg substrate is subjected to RF sputtering etching, and a seedlayer, an underlayer, an intermediate layer, a magnetic layer and an overcoat are successively deposited on the etched surface of the substrate.
The magnetic recording medium produced by the method of the invention have a surface morphology roughness and energy that are determined by the textured substrate and the etching and deposition process. The morphology, roughness and energy of the textured surface can be controlled by adjusting base pressure, the gas composition, RF power and etching time during RF sputtering etching. An optimum modified surface of substrates created by plasma etching with an isotropic etch profile also provides increased flatness allowing a lower magnetic head flying height. The isotropic etching process is preferably controlled by adjusting etching pressure.